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Migrate mailboxes to Exchange Online with a staged migration

Exchange Online
 

Applies to: Exchange Online

Topic Last Modified: 2014-03-05

Use the Migration page (also called the migration dashboard) in the Exchange Administration Center (EAC) or use the Exchange Management Shell and CSV files to migrate batches of Microsoft Exchange on-premises mailboxes to Exchange Online. This migration type is called a staged Exchange migration. It's typically used to migrate mailboxes to Exchange Online over a period of a few weeks or months. Staged migrations are used by organizations that plan to eventually move all mailboxes to Exchange Online and completely transition their on-premises Exchange organization to Exchange Online. A staged migration isn't intended for organizations that want to permanently maintain mailboxes in both their on-premises organization and Exchange Online or that plan to transition all mailboxes to Exchange over a long period of time. An Exchange hybrid deployment is a better solution for maintaining on-premises and cloud-based mailboxes for the long term because it offers features such as secure mail routing between on-premises and Exchange Online organizations, a unified shared address book, Free/Busy and calendar sharing between on-premises and Exchange Online organizations, and the ability to move Exchange Online mailboxes back to the on-premises organization.

You can’t use a staged migration to migrate Exchange 2010 or Exchange 2013 mailboxes to Exchange Online. If you have fewer than 2,000 Exchange 2010 or Exchange 2013 mailboxes in your organization, you can use a cutover Exchange migration. To migrate more than 2,000 Exchange 2010 or Exchange 2013 mailboxes, you have to implement an Exchange hybrid deployment.

For more information about the migration types that you can use to migrate mailboxes to Exchange Online, see the following topics:

Not sure what migration type meets your organization's needs for migrating mailboxes to Exchange Online and Office 365? See the Cloud-Only deployment scenario in the Exchange 2013 Server Deployment Assistant.

To use a staged migration to migrate mailboxes to Exchange Online, you have to replicate user accounts from your on-premises Active Directory directory service to your Office 365 organization. To do this, you have to install and configure the Microsoft Online Services Directory Synchronization tool before you can run a staged migration. After mailboxes are migrated to Exchange Online, user accounts are still managed in your on-premises organization and the Directory Synchronization tool synchronizes your on-premises Active Directory with your Office 365 organization. For more information about the Directory Synchronization tool, see Step 1: Prepare for a staged migration.

Here's what happens when you migrate mailboxes to Exchange Online using a staged migration. Exchange Online does the following for each migration batch that you run:

  • Verifies that the Directory Synchronization tool is enabled for your Office 365 organization.

  • Checks that a mail-enabled user exists in the Office 365 organization for each entry in the CSV file.

  • Converts the mail-enabled users to mailboxes in your Exchange Online organization.

  • Configures mail forwarding by populating the TargetAddress property on the on-premises mailbox with the email address of the Exchange Online mailbox. This enables email sent to an on-premises mailbox to be forwarded to the corresponding Exchange Online mailbox.

  • Copies email messages, contacts, and calendar items from the on-premises mailboxes to the corresponding Exchange Online mailboxes. This process is called initial synchronization. After mailbox items are migrated, the on-premises and Exchange Online mailboxes aren't synchronized. New email sent to the on-premises mailbox is forwarded to the corresponding Exchange Online mailbox.

  • Sends an email message to the administrator when the migration batch has finished initial synchronization. This message lists the number of mailboxes that were successfully migrated and how many couldn’t be migrated. The message also includes links to migration statistics and error reports that contain more detailed information.

  • Estimated time to complete this task: 2-5 minutes to create a migration batch. After the migration batch is started, the duration of the migration will vary based on the number of mailboxes in the batch, the size of each mailbox, and your available network capacity. For information about other factors that affect how long it takes to migrate mailboxes to Exchange Online, see Migration Performance.

  • You need to be assigned permissions before you can perform this procedure or procedures. To see what permissions you need, see the "Migration" entry in the Recipients Permissions topic.

  • For information about keyboard shortcuts that may apply to the procedures in this topic, see Keyboard shortcuts in the Exchange admin center.

  • Out of Office messages aren't migrated with user mailboxes. If a user turns on the Out of Office feature before the migration, the feature will remain enabled on the migrated mailbox but the Out of Office message will be blank. People who send messages to the mailbox won't receive an Out of Office notification. To allow Out of Office notifications to be sent, the user will need to recreate their Out of Office message after their mailbox has been migrated.

TipTip:
Having problems? Ask for help in the Exchange forums. Visit the forums at: Exchange Server, Exchange Online, or Exchange Online Protection..

Be sure to prepare for a staged Exchange migration, especially verifying the ability to successfully connect to your on-premises Exchange organization.

  • Install and configure the Microsoft Online Services Directory Synchronization tool.   The Directory Synchronization tool must be running to perform a staged migration. The tool creates the mail-enabled users in your Exchange Online organization that are converted to mailboxes during the migration. For more information about how to install and activate the Directory Synchronization tool, see Active Directory synchronization: Roadmap.

  • Plan for user identity management.   After on-premises mailboxes are migrated to Exchange Online, the synchronization process continues to update the user attributes for the Exchange Online mailboxes according to changes made in Active Directory on-premises. This means that the source of authority for managing user identity is your on-premises directory. However, after migrating all on-premises mailboxes to Exchange Online, you can configure directory synchronization so that the source of authority is the Office 365 directory service, which allows you to manage mailbox properties in Exchange Online. For more information about user identity management after migrating mailboxes to Exchange Online, see the following topics:

  • Add your on-premises Exchange organization as an accepted domain of your Office 365 organization.   The migration service uses the SMTP address of your on-premises mailboxes to create the email address for the new Exchange Online mailboxes. To run a staged migration, the on-premises domain has to be an accepted domain of your Office 365 organization. For more information, see Add your domain to Office 365.

  • Configure Outlook Anywhere on your on-premises Exchange server.   The email migration service uses RPC over HTTP, or Outlook Anywhere, to connect to your on-premises Exchange server. For information about how to set up Outlook Anywhere for Exchange 2007 and Exchange 2003, see the following:

    ImportantImportant:
    Your Outlook Anywhere configuration must be configured with a certificate issued by a trusted certification authority (CA). It can't be configured with a self-signed certificate. For more information, see How to Configure SSL for Outlook Anywhere.
  • Verify that you can connect to your on-premises Exchange organization using Outlook Anywhere.   Try one of these methods to test your connection settings:

    • Use Microsoft Outlook from outside your corporate network to connect to your on-premises Exchange mailbox.

    • Use the Microsoft Exchange Remote Connectivity Analyzer to test your connection settings. Use the Outlook Anywhere (RPC over HTTP) or Outlook Autodiscover tests.

    • Run the following Shell commands.

      $Credentials = Get-Credential
      
      Test-MigrationServerAvailability -ExchangeOutlookAnywhere -Autodiscover -EmailAddress <email address for on-premises administrator> -Credentials $credentials
      
    • Successfully create a migration endpoint to the Exchange organization that hosts the mailboxes that you're migrating. When you create the endpoint, select Outlook Anywhere as the endpoint type. For more information, see Create migration endpoints.

  • Assign an on-premises user account the necessary permissions to access and modify mailboxes in your Exchange organization.   The on-premises user account that you use to connect to your on-premises Exchange organization (also called the migration administrator) must have the necessary permissions to access and modify the on-premises mailboxes that you want to migrate to Exchange Online. This user account is used to create a migration endpoint to your on-premises organization.

    The following list shows the administrative privileges required to migrate mailboxes using a staged migration. There are three possible options.

    • The migration administrator must be a member of the Domain Admins group in Active Directory in the on-premises organization.

      Or

    • The migration administrator must be assigned the FullAccess permission for each on-premises mailbox AND the WriteProperty permission to modify the TargetAddress property on the on-premises user account.

      Or

    • The migration administrator must be assigned the Receive As permission on the on-premises mailbox database that stores the user mailboxes AND the WriteProperty permission to modify the TargetAddress property on the on-premises user account.

    For more information, see the following.

     

    Exchange 2007

    Exchange 2003

  • Prepare the CSV file.   Identify the group of users whose on-premises mailboxes you want to migrate to Exchange Online. Include these users in a CSV file that will be used to create a migration batch. For information about preparing the CSV file, see Step 2: Create a CSV file to use for a staged migration.

  • Disable Unified Messaging.   If the on-premises mailboxes you're migrating are enabled for Unified Messaging (UM), you have to disable UM on the mailboxes before you migrate them. You can then enable UM on the mailboxes after the migration is complete.

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Identify the group of users whose on-premises mailboxes you want to migrate to Exchange Online. Include these users in a CSV file that will be used to create a migration batch. Each row in the CSV file contains information about an on-premises mailbox. This information is used by Exchange Online to process the migration.

ImportantImportant:
There isn't a limit for the number of mailboxes that you can migrate to the cloud using a staged Exchange migration. However, the CSV file for a migration batch can contain a maximum of 2,000 rows. To migrate more than 2,000 mailboxes, you have to create additional CSV files, and then use each one to create a new migration batch.

Supported attributes

The CSV file for a staged migration supports the following three attributes. Each row, which corresponds to a mailbox, must contain a value for each attribute included in the CSV file.

  • EmailAddress specifies the primary SMTP email address for users’ on-premises mailboxes. Email addresses must use a valid SMTP format, for example, pilarp@tailspintoys.com. This attribute is required.

    ImportantImportant:
    Be sure to use the primary SMTP address for on-premises mailboxes and not user IDs from the cloud-based organization. For example, if the on-premises domain is named tailspintoys.com but the cloud-based email organization is named service.tailspintoys.com you would use the tailspintoys.com domain name for email addresses in the CSV file.
  • Password is the password that will be set on the new Exchange Online mailbox. Any password restrictions that are applied to your cloud-based organization apply to the passwords included in the CSV file. A password has to have a minimum length of eight characters. This attribute is optional.

  • ForceChangePassword specifies whether a user must change the password the first time they sign in to their new cloud-based mailbox. Use either True or False for the value of this parameter. Other values are invalid. This attribute is optional.

    NoteNote:
    If you’ve implemented a single sign-on solution by deploying Active Directory Federation Services 2.0 (AD FS 2.0) in your on-premises organization, you must use False for the value of the ForceChangePassword attribute.

CSV file format

Here's an example of the format for the CSV file. In this example, three on-premises mailboxes are migrated to Exchange Online.

EmailAddress,Password,ForceChangePassword
pilarp@tailspintoys.com,Pa$$w0rd,False
tobyn@tailspintoys.com,Pa$$w0rd,False
briant@tailspintoys.com,Pa$$w0rd,False

The first row, or header row, of the CSV file lists the names of the attributes, or fields, specified in the rows that follow. Each attribute name is separated by a comma.

Each row under the header row represents one user and supplies the information that will be used to migrate the user's mailbox. The attribute values in each row must be in the same order as the attribute names in the header row. Each attribute value is separated by a comma.

Use any text editor, or an application like Microsoft Excel, to create the CSV file. Save the file as a .csv or .txt file.

TipTip:
If the CSV file contains non-ASCII or special characters, save the CSV file with UTF-8 or other Unicode encoding. Depending on the application, saving the CSV file with UTF-8 or other Unicode encoding may be easier when the system locale of the computer matches the language used in the CSV file.

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For a staged migration batch, you have to create an Exchange Outlook Anywhere migration endpoint. A migration endpoint is a management object in Exchange Online that contains the connection settings for the on-premises server that hosts the mailboxes you're migrating and the credentials for an on-premises user account that has the necessary administrative permissions to migrate mailboxes. When you create a migration batch, the information in the migration endpoint is used to connect to the on-premises Exchange server. The migration endpoint also defines the number of mailboxes to migrate simultaneously.

For more information about creating an Exchange Outlook Anywhere migration endpoint, see Create migration endpoints.

TipTip:
Although you can create the first Exchange Outlook Anywhere migration endpoint when you create the first migration batch for a staged migration, we recommend that you create migration endpoints before you create a migration batch. When you create a migration endpoint, Exchange Online tests the connection to the on-premises Exchange server. The migration endpoint isn't created unless Exchange Online can successfully connect to the on-premises server. This lets you troubleshoot and resolve connectivity issues before you create a migration batch. Otherwise, you have to cancel the migration batch and resolve any connectivity issues before you can create a migration batch.

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To create a migration batch, you have to submit a CSV file that contains the information about the mailboxes you want to migrate. You can create and start a maximum of 100 migration batches at a time.

The following procedure will vary based on whether you or another administrator in your Exchange Online organization has created any migration endpoints. We recommend that you create a migration endpoint before you create a migration batch for a staged Exchange migration.

  1. In the EAC, navigate to Recipients > Migration.

  2. Click New Add Icon and then click Migrate to Exchange Online.

  3. On the Select a migration type page, click Staged migration, and then click Next.

  4. On the Select the users page, click Browse to specify the CSV file to use for this migration batch.

    After you select a CSV file, Exchange Online checks the CSV file to make sure that:

    • It isn't empty.

    • It uses comma-separated formatting.

    • It doesn't contain more than 2,000 rows.

    • It includes the required EmailAddress column in the header row.

    • It contains rows with the same number of columns as the header row.

    If any one of these checks fails, you'll get an error that describes the reason for the failure. At this point, you have to fix the CSV file and resubmit it to create a migration batch. After the CSV file is validated, the number of users listed in the CSV file is displayed as the number of mailboxes to migrate.

  5. Click Next.

  6. Depending on whether any Outlook Anywhere migration endpoints have been created for your Exchange Online organization, do one of the following:

    • No migration endpoints have been created: On the Enter on-premises account credentials page, type the user name and password for an account that has the necessary administrative privileges in the on-premises Exchange organization that hosts the mailboxes you're migrating. Use the domain\user name format for the name of the administrator account. Click Next. Exchange Online will use the email address of the user in the first row of the CSV file, the administrative account, and the Autodiscover service to detect the connection settings to your on-premises Exchange organization. If the connection settings are successfully discovered, the fully qualified domain name (FQDN) of your on-premises Exchange server and RPC proxy server are displayed on the Confirm the migration endpoint page. Verify the settings and then click Next. If the test connection to the source server isn't successful, you’re prompted to manually specify the FQDN of your on-premises Exchange server and RPC proxy server. You have to successfully connect to the source server to continue.

      Exchange Online creates a new migration endpoint using the connection settings that were successfully discovered or that you provided manually. By default, this migration endpoint is configured to support 20 maximum concurrent migrations.

      NoteNote:
      It's recommended that you use a migration endpoint that’s created with connection settings that are automatically discovered rather than using settings that you provide manually because the Autodiscover service will be used to connect to each user mailbox in the migration batch. This is important if you have multiple on-premises Exchange servers. Otherwise, you may need to create different migration endpoints that correspond to each on-premises server.
    • One migration endpoint has been created: Exchange Online displays the connection settings from the existing migration endpoint on the Confirm the migration endpoint page. Verify the connection settings, and then click Next.

    • Two or more migration endpoints have been created: Under Select a migration endpoint, select a migration endpoint from the menu and then click Next. The migration service displays the connection settings from the selected migration endpoint on a read-only page. Verify the connection settings, and then click Next.

  7. On the Move configuration page, type the name of the migration batch, and then click Next. This name will be displayed in the list of migration batches on the Migration page after you create the migration batch. Batch names can’t contain spaces or special characters.

  8. On the Start the batch page, do the following:

    • Click Browse to send a copy of the migration reports to other users. By default, migration reports are sent to the administrator who creates the migration batch. You can also access the migration reports from the properties page of the migration batch.

    • Specify one of the following options to start the migration batch after it's created:

      • Automatically start the batch   The migration batch is started as soon as you save the new migration batch. The batch is first marked with a status of Created; the batch is changed to a status of Syncing after it's been started.

      • Manually start the batch later   The migration batch is created but it's not started. The status of the batch is set to Created. To start a migration batch, select it on the migration dashboard and then click Start Start Icon.

  9. Click New to create the migration batch.

    The new migration batch is displayed on the migration dashboard.

You can use the New-MigrationBatch cmdlet to create a migration batch for a staged Exchange migration. Before you can use the Shell to create a migration batch, you have to create a CSV file and a migration endpoint. You can create a migration batch and start it automatically by including the AutoStart parameter. Alternatively, you can create the migration batch and then start it afterwards by using the Start-MigrationBatch cmdlet.

This example creates and starts a migration batch. The example uses the New-MigrationEndpoint cmdlet to create an Outlook Anywhere migration endpoint, and then uses that endpoint to create the migration batch. The migration batch is automatically started by using the AutoStart parameter.

The Get-Credential cmdlet is used to obtain the credentials for the on-premises administrator account, which are required to create the migration batch. When prompted for the user name, you can use either the email address or the domain\user name format for administrator account.

$Credentials = Get-Credential
$MigrationEndpoint = New-MigrationEndpoint -ExchangeOutlookAnywhere -Name EXCH-01Endpoint -Autodiscover -EmailAddress administrator@contoso.com -Credentials $Credentials

New-MigrationBatch -Name StagedBatch1 -SourceEndpoint $MigrationEndpoint.Identity -CSVData ([System.IO.File]::ReadAllBytes("C:\Users\Administrator\Desktop\StagedBatch1.csv")) -AutoStart

This example creates a migration batch and uses the migration endpoint that was created in the previous example. Because the AutoStart parameter isn't included, the migration batch is manually started by using the Start-MigrationBatch cmdlet.

New-MigrationBatch -Name StagedBatch2 -SourceEndpoint EXCH-01Endpoint -CSVData ([System.IO.File]::ReadAllBytes("C:\Users\Administrator\Desktop\StagedBatch2.csv"))

To verify that you've successfully created a migration batch for a staged Exchange migration, do one of the following:

  • In the EAC, navigate to Recipients > Migration. Verify that the batch is displayed in the migration dashboard. If the migration batch was automatically started, the value displayed under Status is Syncing. If you configured the batch to be manually started, the value is Created.

  • In the Shell, run the following command to display information about the new migration batch.

    Get-MigrationBatch
    

    To display detailed information about a migration batch, run the following command.

    Get-MigrationBatch -Identity <identity> | fl
    

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If you create a migration batch and configure it to be manually started, you can start it by using the EAC or the Shell. If a migration batch is currently running when you start another migration batch, the status for the newly started batch is set to Created. As previously stated, when the migration batch is completed, Exchange Online sends an email message to the administrator. This message lists the number of mailboxes that were successfully migrated and how many mailboxes couldn’t be migrated. The message also includes links to migration statistics and error reports that contain more detailed information.

ImportantImportant:
Migration batches with a status of Synced that have no administrator-initiated activity (for example, no administrator has stopped and restarted a migration batch or edited a migration batch) for the last 90 days will be stopped, and then deleted 30 days later if no further action is taken by the administrator.

  1. In the EAC, navigate to Recipients > Migration.

  2. On the migration dashboard, select the batch, and then click Start Start Icon.

Run the following Shell command to start a migration batch.

Start-MigrationBatch -Identity <identity>

If a migration batch was successfully started, its status in the migration dashboard is specified as Syncing. To verify that you've successfully started a migration batch, do one of the following:

  • In the EAC, navigate to Recipients > Migration. Verify that the migration batch was started.

  • In the Shell, run the following command to verify that the migration batch was started.

    Get-MigrationBatch -Identity <identity> | fl Status
    

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After a migration batch has finished running and you’ve verified that all mailboxes in the batch are successfully migrated and the initial synchronization of mailbox items to Exchange Online is complete, it’s recommended that you convert the on-premises mailboxes in the migration batch to mail-enabled users. Why? After a staged Exchange migration, a user has an on-premises mailbox and an Exchange Online mailbox. Because mail sent to the user’s on-premises mailbox is forwarded to their Exchange Online mailbox after migration, users need to connect to their Exchange Online mailboxes to access their email. But if a person uses Outlook to open their mailbox, the Autodiscover service still tries to connect to the on-premises mailbox. After you convert on-premises mailboxes to mail-enabled users, the Autodiscover service uses a mail-enabled user to connect Outlook to the Exchange Online mailbox after the user creates a new Outlook profile.

Another important reason to convert on-premises mailboxes to mail-enabled users is to retain proxy addresses from the Exchange Online mailboxes by copying proxy addresses to the mail-enabled users. This lets you manage cloud-based users from your on-premises organization by using Active Directory. Also, if you decide to decommission your on-premises Exchange organization after all mailboxes are migrated to Exchange Online, the proxy addresses you’ve copied to the mail-enabled users will remain in your on-premises Active Directory.

For more information and to download scripts that you can run to convert mailboxes to mail-enabled users, see the following:

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After all mailboxes in a migration batch have been successfully migrated and you’ve converted the on-premises mailboxes in the batch to mail-enabled users, you're ready to delete a staged migration batch. Be sure to verify that mail is being forwarded to the Exchange Online mailboxes in the migration batch. When you delete a staged migration batch, the migration service cleans up any records related to the migration batch and deletes the migration batch. The batch is removed from the list of migration batches on the migration dashboard.

NoteNote:
You can perform this step and the previous step of converting the on-premises mailboxes to mail-enabled users in any order.

  1. In the EAC, navigate to Recipients > Migration.

  2. On the migration dashboard, select the batch, and then click Delete Delete icon.

Run the following Shell command to delete a migration batch.

Remove-MigrationBatch -Identity <identity>

  1. In the EAC, navigate to Recipients > Migration. Verify that the migration batch is no longer listed on the migration dashboard.

    Or

  2. Run the following command to verify that the migration batch has been deleted.

    Get-MigrationBatch <identity>
    

    The command will either return the migration batch with a status of Removing or it will return an error stating that the migration batch couldn’t be found, verifying that the batch was deleted.

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  • Assign licenses to Office 365 users.   When you migrate a user's mailbox to Exchange Online using a staged migration, an Office 365 user account is created for the user. You have to activate this user account by assigning a license. If you don't assign a license, the mailbox will be disabled when the grace period ends. To assign a license in the Office 365 admin center, see Assign or remove a license.

  • Create an Autodiscover DNS record.   If you’ve migrated all on-premises mailboxes to Exchange Online and are planning to completely transition your on-premises organization to Office 365, you can configure an Autodiscover DNS record for your Office 365 organization to enable users to connect to their new Exchange Online mailboxes with Microsoft Outlook and mobile clients. This new Autodiscover DNS record has to use the same namespace that you’re using for your Office 365 organization. For example, if your cloud-based namespace is contoso.onmicrosoft.com, the Autodiscover DNS record you need to create is autodiscover.contoso.onmicrosoft.com.

    Exchange Online uses a CNAME record to implement the Autodiscover service for Outlook and mobile clients. The Autodiscover CNAME record must contain the following information:

    • Alias   autodiscover

    • Target   autodiscover.outlook.com

    For more information, see Create DNS records for Office 365.

  • Configure your MX record to point to your Office 365 organization.   Until you change your MX record, email sent to users is still routed to their on-premises Exchange mailboxes and then forwarded to the corresponding Exchange Online mailbox. This lets users use their Exchange Online mailbox to access email sent to their on-premises mailbox. When you configure your organization's MX record to point to your Office 365 email organization, all email is sent directly to the Exchange Online mailboxes. For information about configuring MX records, see Create DNS records for Office 365.

    ImportantImportant:
    It can take from 24 to 72 hours for the updated MX record to be propagated. Wait at least 24 hours after you change the MX record and then verify that mail is being routed directly to Exchange Online mailboxes.
  • Decommission on-premises Exchange servers.   After you’ve verified that all email is being routed directly to the Exchange Online mailboxes, have completed the migration of all mailboxes, and no longer need to maintain your on-premises email organization or don’t plan on implementing a single sign-on solution, you can uninstall Exchange from your servers and remove your on-premises Exchange organization.

    ImportantImportant:
    If you implement a single sign-on solution, we strongly recommend that you maintain at least one Exchange server so that you can access Exchange System Manager (Exchange 2003) or the Exchange Management Console/Exchange Management Shell (Exchange 2007, Exchange 2010, and Exchange 2013) to manage mail-related attributes on the on-premises mail-enabled users. For Exchange 2007 and Exchange 2010, the Exchange server that you maintain should have the Hub Transport, Client Access, and Mailbox server roles installed. For Exchange 2013, you should maintain the Mailbox and Client Access servers.

    For more information, see the following:

    CautionCaution:
    Decommissioning Exchange can have unintended consequences. Before decommissioning your on-premises Exchange organization, we recommend that you contact Microsoft Support.

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Here are some tips to optimize your staged Exchange migration:

  • Change the DNS Time-to-Live (TTL) setting on your MX record.   Before you start to migrate mailboxes, change the DNS TTL setting on your current MX record to a shorter interval, such as 3,600 seconds (one hour). Then, when you change your MX record to point to your Office 365 email organization after all mailboxes are migrated, the updated MX record should propagate more quickly because of the shortened TTL interval.

  • Communicate with your users   Let users know ahead of time that you’re migrating their on-premises mailbox to Exchange Online. Consider the following:

    • Ask users to delete old or unnecessary email messages from their Exchange mailbox before migration. This helps reduce the amount of data that has to be migrated and can help reduce the overall migration time. Or, you can clean up their mailboxes yourself.

    • Suggest that users back up their Inbox.

  • Before you start a staged migration batch, tell users they need to switch over to their Exchange Online mailboxes to send and receive email.   Inform users before you start the batch, because they'll stop receiving email sent to their on-premises mailboxes soon after the TargetAddress property is configured to forward mail to their Exchange Online mailbox. Users can sign in to their Exchange Online mailbox as soon as their mail-enabled user object is converted to a mailbox. Also, the Sent Items folder on their on-premises mailbox won't be copied to their Exchange Online mailbox after initial synchronization is complete. So users should start using their Exchange Online mailbox soon after the migration batch is started.

    Be sure to give them the password to their new mailbox (if applicable) and send them links to the following topics to help them connect to their Exchange Online mailbox:

  • Require users to change their password.   In the CSV file, set the ForceChangePassword attribute to True. This forces users to change the password the first time they sign in to their new Exchange Online mailbox and helps ensure that only the user knows the password. Be sure to encourage people to use strong passwords. However, as previously explained, if you’ve implemented a single sign-on solution by deploying AD FS 2.0 in your on-premises organization, you must use False for the value of the ForceChangePassword attribute.

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